In the distribution of electric power, distribution blocks are often employed. These assemblies have widely been used for distributing incoming electrical power to a number of distinct circuits. Applications may vary widely such as power distribution to houses from a common transformer, or in electrical distribution panel boards where the blocks may be mounted on a common rail for distribution in mono-polar or multi-polar applications.
Typically the block includes a connection for a larger conductor cable or bus and a plurality of tap connections for smaller conductors. The bare ends of the conductors are inserted in socket ports or holes and held in place typically by a clamp or binding screw threaded in a hole perpendicular to the socket receiving the conductor.
One of the problems with these types of distribution blocks is that many of the tap connections are added at a later time after the system is in operation and the block energized. To make the connection safely the system may require to be shut down, and this in turn may create a raft of problems, particularly if the power is shut down for any length of time.
In order to protect the block from incidental contact many are enclosed in insulating enclosures or cases which protect the block from direct contact. To make a connection the case may be provided with large windows or ports or even hinged covers which may be opened for access, or the cases may be removed entirely, all of which permits finger contact with the block by the installer.
The use of insulating cases makes the proper installation of primary and tap connections more problematic. In a connection using a typical blind socket port or hole the installer simply inserts the bare or stripped end of the conductor into the socket until resistence is felt and then tightens the binding screw. It may not be determined that an improper connection was made until the power is turned on again or until the connection fails because the bare end of the conductor wasn't properly positioned with respect to the binding screw. The conductor may have hung-up on an obstruction which was not the blind end of the hole or port. If the conductor is inserted too far, the projecting end may interfere with or obstruct something else, and the binding screw may be tightened on insulation. Moreover non-uniform projecting conductors create a mess, particularly when all the taps are used making service and inspection difficult.
It would accordingly be advantageous for the installer to be able to have both the abutment afforded by the blind end of the port and a visual check to see that the conductor is properly inserted or placed before the binding screw is tightened. In this manner, ensured uniform connections can be made for each of the taps, with the ends of the conductors projecting beyond the screws a uniform distance, and not too far or not far enough.
Another problem with insulating cases involves loose screws. If there is enough clearance between the top of the block and the cover of the case, the binding screws may be backed out too far and become disengaged with the threaded socket. The result is a loose screw inside the insulating case and the only way it can be repositioned or reinserted in its threaded socket is to open the case, which in turn compromises the goal of providing a finger safe assembly without shutting off the power.
It would also of course be desirable that these uniform tap connections could all be made without turning off the power or opening an insulating case. It would therefore be desirable to be able to make such uniform connections having both the visual and physical abutment check without finger contact with the block and without opening the case. A power distribution block with such connections which is finger-safe once the incoming line is installed is highly desirable.
It would also be advantageous to have an assembly where the screws could not be backed out far enough to become disengaged from their respective threaded sockets. But if they did become disengaged, without becoming loose or losing their alignment with their respective threaded socket, and all without losing both the visual and physical check of proper placement of the conductor within the gallery or port of the block.